1. Field of the Invention
The present invention relates to a planar light source device comprising a light guide having a light exit surface on which a dot pattern is formed, a liquid crystal display apparatus using the planar light source device, and a method for manufacturing them.
2. Description of the Related Art
In recent years, liquid crystal display apparatuses are utilized in various fields, making full use of its advantage of thinness and lightness.
Generally, a liquid crystal display apparatus has a liquid crystal display panel which displays an input image, and a planar light source device which illuminates the liquid crystal display panel from behind it. The planar light source device comprises a light source, a light guide which receives the light emitted from the light source and exits the light, and a reflector which causes the light emitted from the light source to be incident on the light guide.
The light exit surface of the light guide is covered with a plurality of optical sheets to uniform the brightness of light or improve the brightness, and the surface opposite to the light exit surface is covered with a reflection sheet. Recently, in order to reduce the number of optical sheets, a type of planar light source device has been developed, in which a light guide has a grained surface having a convex dot pattern as a light exit surface. The dot pattern on the light exit surface is formed such that the density of dots increases as the distance from the light source increases. With this arrangement, the planar light that exits from the light exit surface is uniformed.
In the planar light source device described above, the reflector has two ends, which form openings through which light emitted from the light source is discharged. The reflector surrounds the light source such that the two ends sandwich the light guide and the reflection sheet in the thickness direction thereof. With this structure, the light emitted from the light source can be utilized efficiently, and therefore, the brightness can be increased.
When the light is discharged from the reflector, the positional relationship between the reflector and the light guide greatly influences the evenness of the brightness of the emitted light. The conventional planar light source device has the following problem: since it is difficult to position the reflector relative to the light guide, positioning of the central portion of the reflector especially requires a long time.
To solve the above problem, a method of forming a step or groove in the light guide has been proposed to make the positioning of the reflector easier.
The above method requires that a step or groove be formed on the light exit surface of the light guide. Therefore, this method is not suitable for the case of using a light guide, which has a grained surface as the light exit surface.